Dr. Eugen Weschke,Hahn-Meitner-Institut, Berlin, Germany.

ABSTRACT Resonant x-ray scattering in the soft x-ray region exploits strong dipole excitations of core electrons into 3d and 4f states of important materials and is now becoming a more common tool to study complex and subtle ordering phenomena in condensed matter. The method suffers from two major drawbacks: The wavelengths of the resonance energies are comparably large (of the order of one nanometer) and the absorption of the x-rays in air and in the samples is substantial. However, these disadvantages are by far more than compensated by the chemical selectivity and the very high sensitivity to particular electronic states that can be adressed at resonance. And fortunately, there is plenty of relevant ordering phenomena on a nanometer length scale in relevant materials. With a recently developed UHV diffractometer, we have carried out resonant scattering experiments that make use of different parts of the resonant scattering amplitude and that will be discussed: (i) Resonant magnetic scattering factors of the order of 200r0 provide magnetic contrast to study the magnetization in an antiferromagnetic thin film with atomic layer resolution. (ii) The complex interplay of 4f and 3d magnetic order in multiferroic manganites and relevant magnetic moment directions in the various phases are characterized by the polarization dependence of resonant magnetic scattering. (iii) Charge order in La1.8-xEu0.2SrxCuO4 (LESCO) is studied at the oxygen K resonance as a function of Sr doping x, in this way directly addressing the ordering of the oxygen holes.